I. Field of the Invention
The present invention is directed toward detecting defects on substrates such as transparent and coated glass substrates, silicon wafers, and magnetic disk media and more particularly toward measuring wear, surface roughness, scratches, particles, stains, pits, mounds, surface topography, step heights, and inclusions by shining bright light along a direction on the surface of the substrate.
II. Description of Background Art
Coated thin film disks are used in a variety of industries including the semiconductor and the magnetic hard disk industry. A computer hard disk (magnetic storage device) is a non-volatile memory device that can store large amounts of data. One problem that the manufacturers of hard disks experience is how to maximize the operating life of a hard disk. When a hard disk fails the data stored therein may be difficult, expensive, or impossible to retrieve. Failure of a hard disk may be caused by defects on the surface of the thin film disk. It is important to be able to detect and classify these defects in order to prevent disk drive failure and to control the manufacturing process.
A schematic of a thin film disk used in magnetic storage devices is shown in FIG. 1. It includes a magnetic thin film (layer) 106, which is deposited upon a substrate 108 (typically a NiP plated Al—Mg alloy or glass). The magnetic thin film 106 can be protected by a thin film of carbon 104 (carbon layer), for example, whose thickness is typically 20 to 200 Angstroms (Å). The carbon layer 104 is typically coated with a thin layer (10 to 30 Angstroms) of a fluorocarbon lubricant 102 (lubricant layer). The lubricant layer 102 serves to increase the durability of the underlying carbon layer 104 particularly when the magnetic read/write head contacts the disk, for example when the disk drive is turned off. The hard disk drive industry has been dramatically improving storage capacity by flying the thin film head closer to the surface of the thin film disk. As a result even very small defects can cause a hard drive to fail. These defects may be topographic such as scratches, pits, mounds, or particles or they may be non-topographic such as stains or inclusions. It is useful to measure all these types of defects to control the disk manufacturing process and improve disk drive manufacturing yield.
A schematic of a semiconductor wafer is shown in FIG. 2. The structure of a semiconductor wafer can be very complex and FIG. 2 shows only a typical structure of a wafer that is undergoing the copper dual damascene process. In FIG. 2, 201 is the copper layer 202 is the second plasma enhanced chemical vapor deposited (PECVD) oxide layer, 203 is the first PECVD oxide layer and 204 is the silicon substrate. The copper layer 201 is polished down using a chemical mechanical polishing (CMP) process until only the via holes and copper lines remain. The problem is that the CMP process can leave residual copper, nitride, or CMP slurry on the surface of the wafer. In addition, stains, particles, scratches, and micro-waviness may be present on the polished wafer. It is useful to detect and measure such defects to control the process of making the wafer. Fewer defects will also mean greater wafer yields at the end of the process. The problem in the hard disk, semiconductor and photonics industries is to inspect these magnetic disks and wafers for defects such as particles, scratches, pits, mounds, stains, topographic irregularities and inclusions. Conventional techniques to solve these problems are discussed in U.S. Pat. No. 4,674,875, 5,694,214, 5,748,305, and 6,157,444 that are all incorporated by reference herein in their entirety. These patents describe techniques to measure defects using essentially sophisticated scatterometers and reflectometers. Prior art systems also measure defects by shining white light on a surface at a high angle of incidence; the image of the surface is then captured with a charge couple device (CCD) camera and analyzed for defects. None of these systems enables the detection and classification of surface features or defects by controlling the angle of the illumination plane of incidence with respect to the features or defects in order to detect and differentiate topological and non-topological defects.
Thus, what is needed is a system and method for examining the surface of substrates, such as silicon wafers or magnetic disk media, for topological and non-topological defects and features by controlling the angle of illumination plane of incidence with respect to the features or defects.